Light-emitting semiconductor device using group III nitrogen compound

ABSTRACT

A light-emitting semiconductor device ( 10 ) consecutively includes a sapphire substrate ( 1 ), an AlN buffer layer ( 2 ), a silicon (Si) doped GaN n + -layer ( 3 ) of high carrier (n-type) concentration, a Si-doped (Al x3 Ga 1-x3 ) y3 In 1-y3 N n + -layer ( 4 ) of high carrier (n-type) concentration, a zinc (Zn) and Si-doped (Al x2 Ga 1-x2 ) y2 In 1-y2 N emission layer ( 5 ), and a Mg-doped (Al x1 Ga 1-x1 ) y1 In 1-y1 N p-layer ( 6 ). The AlN layer ( 2 ) has a 500 Å thickness. The GaN n + -layer ( 3 ) has about a 2.0 μm thickness and a 2×10 18 /cm 3  electron concentration. The n + -layer ( 4 ) has about a 2.0 μm thickness and a 2×10 18 /cm 3  electron concentration. The emission layer ( 5 ) has about a 0.5 μm thickness. The p-layer  6  has about a 1.0 μm thickness and a 2×10 17 /cm 3  hole concentration. Nickel electrodes ( 7, 8 ) are connected to the p-layer ( 6 ) and n + -layer ( 4 ), respectively. A groove ( 9 ) electrically insulates the electrodes ( 7, 8 ). The composition ratio of Al, Ga, and In in each of the layers ( 4, 5, 6 ) is selected to meet the lattice constant of GaN in the n + -layer ( 3 ). The LED ( 10 ) is designed to improve luminous intensity and to obtain purer blue color.

The present Applicant is a Divisional Application of U.S. patentapplication Ser. No. 11/328,079 filed on Jan. 10, 2006, which is aDivisional Application of U.S. patent application Ser. No. 11/143,664filed on Jun. 3, 2005, which in turn is a Divisional Application of U.S.patent application Ser. No. 09/783,035 filed on Feb. 15, 2001, which inturn is a Divisional Application of U.S. patent application Ser. No.09/379,621 filed on Aug. 24, 1999, now U.S. Pat. No. 6,256,726, which inturn is a Continuation Application of U.S. patent application Ser. No.08/408,164 filed Mar. 21, 1995.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a light-emitting semiconductor devicethat emits blue light and uses a group III nitrogen compound.

2. Description of the Prior Art

It has been known that an aluminum gallium indium nitride (AlGaInN)compound semiconductor may be used to obtain a light-emitting diode(LED) which emits blue light. This semiconductor device is usefulbecause of its high luminous efficiency resulting from direct electrontransition and because of its ability to emit blue light, which is oneof the three primary colors.

Irradiating an electron beam into an i-layer to which magnesium (Mg) isdoped and heat treatment is carried out enables the i-layer to have ap-type layer of the AlGaInN semiconductor device. As a result, a LEDwith a double hetero p-n junction structure includes an aluminum galliumnitride (AlGaN) p-layer, a zinc (Zn) doped indium gallium nitride(InGaN) emission layer and an AlGaN n-layer, becomes useful instead ofconventional LED of metal insulator semiconductor (MIS) structure whichincludes an n-layer and a semi-insulating i-layer.

The conventional LED with a double hetero p-n junction structure isdoped with Zn as an emission center. Luminous intensity of this type ofLED has been improved fairly. Still, there exists a problem in luminousefficiency and further improvement is necessary.

The emission mechanism of a LED with an emission layer doped with onlyZn, or only an acceptor impurity, as the emission center is electrontransition between conduction band and acceptor energy levels. However,a large difference of their energy levels makes recombination ofelectrons through deep levels dominant which deep level recombinationdoes not contribute to emission. This results in lower luminousintensity. Further, the wavelength of light from the conventional LED isabout 380 to 440 nm, or shorter than that of pure blue light.

Further, the emission layer doped with Zn as the emission centerexhibits semi-insulative characteristics. Its emission mechanism isexplained by recombination of an electron through acceptor levelinjected from an n-layer and a hole injected from a p-layer. However,the diffusion length of the hole is shorter than that of the electron.It results in high ratio of holes disappearing in a non-emission processbefore recombination of the hole and electron occurs in the emissionlayer. This phenomenon impedes higher luminous intensity.

SUMMARY OF THE INVENTION

It is an object of the present invention to solve the above problem andimprove the luminous intensity of the LED of AlGaInN semiconductor, orobtain enough spectrum to emit a purer blue light.

According to the first aspect of the invention, there is provided alight-emitting semiconductor device comprising:

an n-layer with n-type conduction of group III nitride compoundsemiconductor satisfying the formula Al_(x3)Ga_(y3)In_(1-x3-y3)N,inclusive of x3=0, y3=0 and x3=y3=0,

a p-layer with p-type conduction of group III nitride compoundsemiconductor satisfying the formula Al_(x1)Ga_(y1)In_(1-x1-y1)N,inclusive of x1=0, y1=0 and x1=y1=0,

an emission layer of group III nitride compound semiconductor satisfyingthe formula Al_(x2)Ga_(y2)In_(1-x2-y2)N, inclusive of x2=0, y2=0 andx2=y2=0;

the junction layer of the n-layer, the p-layer, and the emission layerbeing any one of a homo-junction, structure, a single hetero-junctionstructure, and a double hetero-junction structure; and

wherein the emission layer is formed between the n-layer and thep-layer, and doped with both a donor and an acceptor impurity.

It is preferable that the donor impurity is one of the group IV elementsand that the acceptor impurity is one of the group II elements.

Preferable combinations of a donor and an acceptor impurity includesilicon (Si) and cadmium (Cd), silicon (Si) and zinc (Zn), and silicon(Si) and magnesium (Mg), respectively.

The emission layer can be controlled to exhibit any one of n-typeconduction, semi-insulative, and p-type conduction depending on theconcentration ratio of a donor impurity and an acceptor impurity dopedthereto.

Further, the donor impurity can be one of the group VI elements.

Further, it is desirable to design the composition ratio of Al, Ga, andIn in the n-layer, p-layer, and emission layer to meet each of thelattice constants of the three layers to an n⁺-layer of high carrierconcentration on which the three layers are formed.

Further, a double hetero-structure sandwiching of the emission layer ofp-type conduction by the n-layer and p-layer improves luminousefficiency. Making the concentration of acceptor impurity larger thanthat of the donor impurity and processing by electron irradiation orheat treatment changes the emission layer to exhibit p-type conduction.Magnesium, an acceptor impurity, is especially efficient for obtainingp-type conduction.

Further, doping any combinations of the described acceptor and donorimpurity to an emission layer of p-type conduction also improvesluminous efficiency. The luminous mechanism doped with acceptor anddonor impurities is due to recombination of an electron at donor leveland a hole at the acceptor level. This recombination occurs within theemission layer, so that luminous intensity is improved.

Further, a double hetero-junction structure of a triple-layersandwiching the emission layer having a narrower bad gap by the n-layerand p-layer having a wider band gap improves luminous intensity. Sincethe emission layer and the p-layer exhibit p-type conduction, valencebands of those layers are successive even without applying externalvoltage. Consequently, holes readily highly exist within the emissionlayer. In contrast, conduction bands of the n-layer and the emissionlayer are not successive without applying an external voltage. Applyinga voltage enables the conduction bands to be successive and electrons tobe injected deeper into the emission layer. Consequently, the number ofinjected electrons into the emission layer increases ensuringrecombination with holes and a consequent improvement in luminousintensity.

Other objects, features, and characteristics of the present inventionwill become apparent upon consideration of the following description inthe appended claims with reference to the accompanying drawings, all ofwhich form a part of the specification, and wherein referenced numeralsdesignate corresponding parts In the various figures.

BRIEF DESCRIPTION OF THE DRAWING

In the accompanying drawings:

FIG. 1 is a diagram showing the structure of the LED embodied in Example1;

FIGS. 2 through 7 are sectional views illustrating successive steps ofproducing the LED embodied in Example 1;

FIG. 8 is a diagram showing the structure of the LED embodied in Example2;

FIG. 9 is a diagram showing the structure of the LED embodied in Example3;

FIG. 10 is a diagram showing the structure of the LED embodied inExample 4;

FIG. 11 is a diagram showing the structure of the LED embodied inExample 5;

FIGS. 12 and 13 are diagrams showing the structure of the LED embodiedin Example 6;

FIG. 14 is a diagram showing the structure of the LED embodied inExample 7; and

FIGS. 15 and 16 are diagrams showing the structure of the LED embodiedin Example 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The invention will be more fully understood by reference to thefollowing examples.

Example 1

FIG. 1 shows a LED 10 embodied in Example 1. It has a sapphire (Al₂O₃)substrate 1 upon which the following five layers are consecutivelyformed: an AlN buffer layer 2; a silicon (Si) doped GaN n⁺-layer 3 ofhigh carrier (n-type) concentration; a Si-doped(Al_(x2)Ga_(1-x2))_(y2)In_(1-y2)N n⁺-layer 4 of high carrier (n-type)concentration; a cadmium (Cd) and Si-doped(Al_(x1)Ga_(1-x1))_(y1)In_(1-y1)N emission layer 5; and a Mg-doped(Al_(x2)Ga_(1-x2))_(y2)In_(1-y2)N p-layer 6. The AlN layer 2 has 500 Åthickness. The GaN n⁺-layer 3 is about 2.0 μm, in thickness and has a2×10¹⁸/cm³ electron concentration. The n⁺-layer 4 is about 2.0 μm inthickness and has a 2×10¹⁸/cm³ electron concentration. The emissionlayer 5 is about 0.5 μm in thickness. The i-layer 6 is about 1.0 μm inthickness and has a 2×10¹⁷/cm³ hole concentration. Nickel electrodes 7and 8 are connected to the p-layer 6 and the n⁺-layer 4, respectively.They are electrically insulated by a groove 9.

The LED 10 is produced by gaseous phase growth, called metal organicvapor phase epitaxy referred to as MOVPE hereinafter.

The gases employed in this process are ammonia (NH₃), a carrier gas (H₂or N₂), trimethyl gallium (Ga(CH₃)₃) (TMG hereinafter), trimethylaluminum (Al(CH₃)₃) (TMA hereinafter), trimethyl indium (In(CH₃)₃) (TMIhereinafter), dimethylcadmium ((Cd(CH₃)₂) (DMCd hereinafter), silane(SiH₄), diethylzinc ((C₂H₅)₂Zn) (DEZ hereinafter) andbiscyclopentadienyl magnesium (Mg(C₅H₅)₂) (CP₂Mg hereinafter).

The single crystalline sapphire substrate 1, whose main surface ‘a’ wascleaned by an organic washing solvent and heat treatment, was placed ona susceptor in a reaction chamber for the MOVPE treatment. Then thesapphire substrate 1 was etched at 1100° C. by a vapor of H₂ fed intothe chamber at a flow rate of 2 liter/min. under normal pressure for aperiod of 5 min.

On the etched sapphire substrate 1, a 500 Å thick AlN buffer layer 2 wasepitaxially formed on the surface ‘a’ under conditions of lowering thetemperature in the chamber to 400° C., keeping the temperature constant,and supplying H₂, NH₃ and TMA for a period of about 90 sec. at a flowrate of 20 liter/min., 10 liter/min., and 1.8×10⁻⁵ mol/min.,respectively. On the buffer layer 2, about a 2.2 μm thick Si-doped GaNn⁺-layer 3 of high carrier concentration with an electron concentrationof about 2×10¹⁸/cm³ was formed under conditions of keeping thetemperature of the sapphire substrate 1 at 1150° C. and supplying H₂,NH₃, TMG, and diluted silane to 0.86 ppm by H₂ for thirty minutes at aflow rate of 20 liter/min., 10 liter/min., 1.7×10⁻⁴ mol/min. and 200ml/min., respectively.

The following manufacturing process provides for an emission layer 5 asan active layer, an n⁺-layer 4 of high carrier concentration, and ap-layer 6 as a clad layer; the LED 10 is designed to emit at a 450 nmwavelength peak in the luminous spectrum and have luminous centers of Cdand Si.

On the n⁺-layer 3, about a 0.5 μm thick Si-doped(Al_(0.47)Ga_(0.53))_(0.9)In_(0.1)N n⁺-layer 4 of high carrierconcentration with an electron concentration of 1×10¹⁸/cm³ was formedunder conditions of keeping the temperature of the sapphire substrate 1at 850° C. and supplying N₂ or H₂, NH₃, TMG, TMA, TMI, and dilutedsilane to 0.86 ppm by H₂ for 60 min. at a flow rate of 10 liter/min., 10liter/min., 1.12×10⁻⁴ mol/min., 0.47×10⁻⁴ mol/min., 0.1×10⁻⁴ mol/min.and 10×10⁻⁹ mol/min., respectively.

On the n⁺-layer 4, about a 0.5 μm thick Cd andSi-doped(Al_(0.3)Ga_(0.7))_(0.94)In_(0.06)N emission layer 5 was formedunder conditions of keeping the temperature of the sapphire substrate 1at 850° C. and supplying N₂ or H₂, NH₃, TMG, TMA, TMI, DMCd, and dilutedsilane to 0.86 ppm by H₂ for 60 min. at a flow rate of 20 liter/min., 10liter/min., 1.53×10⁻⁴ mol/min., 0.47×10⁻⁴ mol/min., 0.02×10⁻⁴ mol/min.,2×10⁻⁷ mol/min. and 10×10⁻⁹ mol/min., respectively. At this stage, thelayer 5 exhibited high resistivity. The impurity concentrations of theCd and the Si doped to the emission layer 5 were 5×10¹⁸/cm³ and1×10¹⁸/cm³, respectively.

On the emission layer 5, about a 1.0 μm thick Mg-doped(Al_(0.47)Ga_(0.53))_(0.9)In_(0.1)N p-layer 6 was formed underconditions of keeping the temperature of the sapphire substrate 1 at1000° C. and supplying N₂ or H₂, NH₃, TMG, TMA, TMI, and CP₂Mg for 120min. at a flow rate of 20 liter/min., 10 liter/min., 1.12×10⁻⁴ mol/min.,0.47×10⁻⁴ mol/min., 0.1×10⁻⁴ mol/min. and 2×10⁻⁴ mol/min., respectively.Resistivity of the p-layer 6 was 10⁸ Ω·cm or more exhibiting insulativecharacteristics. The impurity concentration of the Mg-doped into thep-layer 6 was 1×10²⁰/cm³.

Then, electron rays were uniformly irradiated into the p-layer 6 using areflective electron beam diffraction device. The irradiation conditionswere set at 10 KV for the accelerating voltage, 1 μA for the samplecurrent, 0.2 mm/sec. for the speed of the beam scanning, 60 μmφ for thebeam aperture, and at 5.0×10⁻⁵ Torr vacuum. This irradiation changed theinsulative p-layer 6 into a p-type conductive semiconductor with a holeconcentration of 2×10¹⁷/cm³ and a resistivity of 2 Ω·cm. Thereby, awafer with multi-structural layers was obtained as shown in FIG. 2.

The following FIGS. 3 to 7 show sectional views of an individual elementon the wafer. In actual practice and in accordance with industry custom,a wafer with a large number of elements thereon is treated by thefollowing process and divided or diced into individual elements.

A 2000 Å thick SiO₂ layer 11 was formed on the p-layer 6 by sputtering.Then, the layer 11 was coated with a photoresist layer 12. Two selectedparts or areas of the photoresist layer 12, named A and B, were removedby photolithography as shown in FIG. 3. The part or area A is anelectrode forming part which corresponds to a place where a hole 15,shown in FIG. 5, is formed extending to and into the n⁻-layer 4 of highcarrier concentration. The part or area B corresponds to a place where agroove 9 shown in FIGS. 5 and 6 is formed for insulating or electricallyinsulating the part or area A from an electrode in contact with thep-layer 5.

As shown in FIG. 4, two parts of the SiO₂ layer 11 which were notcovered with the photoresist layer 12 were etched off by an etchingliquid such as hydrofluoric acid. Then, the exposed part of thefollowing successive three layers from the surface of the device, thep-layer 6, the emission layer 5, and the upper part of the n⁺-layer 4 ofhigh carrier concentration, were removed by dry etching, or supplying ahigh-frequency power density of 0.44 W/cm² and BCl₃ gas of 10 ml/min. ata vacuum degree of 0.04 Torr as shown in FIG. 5. After that, dry etchingwith argon (Ar) was carried out on the device. Consequently, a hole 15for forming an electrode reaching the n⁺-layer 4 of high carrierconcentration and a groove 9 for insulation are formed.

The SiO₂ layer 11 remaining on the p-layer 6 was removed by hydrofluoricacid as shown in FIG. 6. A nickel (Ni) layer 13 was laminated on theentire surface of the device by vapor deposition. Thus, the so-formed Nilayer 13 in the hole 15 is in electrical contact with the n⁺-layer 4 ofhigh carrier concentration. A photoresist 14 was deposited on the Nilayer 13 and, then, was selectively etched off by photolithography asshown in FIG. 7 leaving patterns of configuration for electrodesconnected to the n⁺-layer 4 of high carrier concentration and thep-layer 6, respectively.

Using the photoresist 14 as a mask, the exposed part or area of the Nilayer 13 from the photoresist 14 was etched off by an etching liquidsuch as nitric acid. At this tine, the nickel layer 13 laminated in thegroove 9 was also removed completely. Then, the photoresist layer 14 wasremoved by a photoresist removal liquid such as acetone. There wereformed two electrodes, the electrode 8 for the n⁺-layer 4 of highcarrier concentration and the electrode 7 for the p-layer 6. A wafertreated with the above-mentioned process was divided or diced into eachelement which shows a gallium nitride light-emitting diode with a p-njunction structure as shown in FIG. 1.

The obtained LED 10 was found to have a luminous intensity of 100 mcdand a wavelength of 450 nm by driving current of 20 mA.

The emission layer 5 preferably contains impurity concentrations of Cdand Si within a range of 1×10¹⁷/cm³ to 1×10²⁰/cm³, respectively, inorder to improve luminous intensity. It is further desirable that theconcentration of Si is smaller than that of Cd by ten to fifty percent.

In order to make the band gap of the emission layer 5 smaller than thoseof its respective adjacent two layers, i.e., the p-layer 6 and then⁺-layer 4 of high carrier concentration, a double hetero-junctionstructure was utilized for the LED 10 in this embodiment. Alternatively,a single hetero-junction structure can be utilized.

Further, it is preferable that the composition ratio of Al, Ga, and Inin the respective three layers 4, 5, and 6 is selectively designed tomeet the lattice constants of their layers 4, 5, and 6 with the latticeconstant of GaN in the n⁺-layer 3 of high carrier concentration asprecisely as possible.

Example 2

FIG. 8 shows a LED 10 utilized in Example 2. The emission layer 5 inExample 1 was doped with Cd and Si. In this Example 2, an emission layer5 is doped with Zn and Si.

A manufacturing process of a sapphire substrate 1, the formation of theAlN buffer layer 2 and the n⁺-layers 3 was similar to that discussed inthe previous example.

About a 0.5 μm thick Si-doped (Al_(0.3)Ga_(0.7))_(0.94)In_(0.06)Nn⁺-layer 4 of high carrier concentration with an electron concentrationof 2×10¹⁹/cm³ was formed on the n⁺-layer 3 under conditions of loweringthe temperature in the chamber to 800° C., keeping the temperatureconstant, and supplying N₂, NH₃, TMG, TMA, TMI, and diluted silane to0.86 ppm by H₂ for 120 min. at a flow rate of 20 liter/min., 10liter/min., 1.12×10⁻⁴ mol/min., 0.47×10⁻⁴ mol/min., 0.1×10⁻⁴ mol/min.,and 10×10⁻⁹ mol/min., respectively.

About a 0.5 μm thick Si- and Zn-doped(Al_(0.09)Ga_(0.91))_(0.99)In_(0.01)N emission layer 5 was formed on then⁺-layer 4 under conditions of lowering the temperature in the chamberto 1150° C., keeping it constant, and supplying N₂, NH₃, TMG, TMA, TMI,diluted silane to 0.86 ppm by H₂, and DEZ for 7 min. at a flow rate of20 liter/min., 10 liter/min., 1.53×10⁻⁴ mol/min., 0.47×10⁻⁴ mol/min.,0.02×10⁻⁴ mol/min. and 10×10⁻⁹ mol/min., and 2×10⁻⁴ mol/min.,respectively. The impurity concentration of the Zn- and Si-doped intothe emission layer 5 was 2×10¹⁸/cm³ and 1×10¹⁸/cm³, respectively.

About a 1.0 μm thick Mg-doped (Al_(0.3)Ga_(0.7))_(0.94)In_(0.06)Np-layer 6 was formed on the emission layer 5 under conditions oflowering the temperature in the chamber to 1100° C., keeping thetemperature constant, and supplying N₂, NH₃, TMG, TMA, TMI, and CP₂Mg ata flow rate of 20 liter/min., 10 liter/min., 1.12×10⁻⁴ mol/min.,0.47×10⁻⁴ mol/min., 0.1×10⁻⁴ mol/min., and 2×10⁻⁴ mol/min.,respectively. The impurity concentration of Mg doped into the p-layer 6was 1×10²⁰/cm³. At this stage, the p-layer 6 remained insulative with aresistivity of 10⁸ Ω·cm or more.

Then, the p-layer 6 was processed to have p-type conduction by electronbeam irradiation under the same conditions described in Example 1. Thesubsequent process steps of forming the electrodes are the same as thatdescribed in the previous example. The so-obtained LED 10 was found tohave a luminous intensity of 1000 mcd and a wavelength of 450 nm bydriving current of 20 mA.

Example 3

FIG. 9 shows a structural view of a LED 10 embodied in Example 3. TheLED 10 in Example 3 was manufactured by additionally doping Mg to theemission layer 5 of the LED in Example 2. Other layers and electrodeswere manufactured in the same way as those in Example 2.

CP₂Mg was fed at a flow rate of 2×10⁻⁴ mol/min. into a chamber inaddition to the gasses employed in Example 2 in order to manufacture theemission layer 5 in Example 3. The emission layer 5 was about 0.5 μmthick comprising Mg, Zn, and Si-doped(Al_(0.09)Ga_(0.91))_(0.99)In_(0.01)N. Its resistivity was 10⁸ Ω·cmremaining insulative. Impurity concentration of Mg, Zn, and Si was1×10¹⁹/cm³, 2×10¹⁸/cm³, and 1×10¹⁸/cm³, respectively.

Then, both of the emission layer 5 and a p-layer 6 were subject toelectron beam irradiation with the electron beam diffraction deviceunder as same conditions as in Example 1. Thus, the emission layer 5 andthe p-layer 6 turned into layers exhibiting p-type conduction with ahole concentration of 2×10¹⁷/cm³ and resistivity of 2 Ω·cm.

Example 4

FIG. 10 shows a structural view of a LED 10 embodied in Example 4. Inthis example, an emission layer 5 includes GaN and had a singlehetero-junction structure. Namely, one junction comprises a heavilySi-doped n⁺-layer 4 of high carrier concentration and a Zn- and Si-dopedGaN emission layer 5, and another junction includes the GaN emissionlayer 5 and a Mg-doped Al_(0.1)Ga_(0.9)N p-layer 61 with p-typeconduction. In this example, the Mg-doped GaN p-layer 62 as a contactlayer is formed on the p-layer 61. An insulation groove 9 is formedthrough the contact layer 62, the p-layer 61 and the emission layer 5.

The LED 10 in this example has a sapphire substrate 1 upon which thefollowing five layers are consecutively formed: an AlN buffer layer 2; aSI-doped GaN n⁺-layer 4 of high carrier (n-type) concentration; a Zn andSi-doped GaN emission layer 5, Mg-doped Al_(0.1)Ga_(0.9)N p-layer 61,and Mg-doped GaN contact layer 62. The AlN layer 2 has a 500 Åthickness. The GaN n⁺-layer 4 has about a 4.0 μm thickness and a2×10¹⁸/cm³ electron concentration. The emission layer 5 has about a 0.5μm thickness. The p-layer 61 has about a 0.5 μm thickness and a2×10¹⁷/cm³ hole concentration. The contact layer 62 has about a 0.5 μmthickness and a 2×10¹⁷/cm³ hole concentration. Nickel electrodes 7 and 8are formed to connect to the contact layer 62 and the n⁺-layer 4 of highcarrier concentration, respectively. The two electrodes are electricallyinsulated by a groove 9.

Here is explained a manufacturing process of the LED 10. The sapphiresubstrate 1 and the AlN buffer layer 2 were prepared by the same processdescribed in detail in Example 1. On the AlN buffer layer 2, about a 4.0μm thick Si-doped GaN n⁺-layer 4 of high carrier concentration with anelectron concentration of 2×10¹⁸/cm³ was formed under conditions oflowering the temperature in the chamber to 1150° C., keeping thetemperature constant and supplying N₂, NH₃, TMG, and diluted silane to0.86 ppm by H₂ for 60 min. at a flow rate of 20 liter/min., 10liter/min., 1.7×10⁻⁴ mol/min., 0.47×10⁻⁴ mol/min., 0.1×10⁻⁴ mol/min.,and 10×10⁻⁹ mol/min., respectively.

The following manufacturing process and composition ratio provide forthe three layers, the emission layer 5 as an active layer, the p-layer62 as a clad layer, and the contact layer 62. The LED is designed tohave 430 nm wavelength at peak in the luminous spectrum and haveluminous centers of Zn and Si.

About a 0.5 μm thick Zn- and Si-doped GaN emission layer 5 was formed onthe n⁺-layer 4 under conditions of lowering the temperature in thechamber to 1000° C., keeping it constant and supplying N₂ or H₂, NH₃.TMG, DMZ, and diluted silane to 0.86 ppm by H₂ for 8 min. at a flow rateof 20 liter/min., 10 liter/min., 1.53×10⁻⁴ mol/min., 2×10⁻⁷ mol/min.,and 10×10⁻⁹ mol/min., respectively.

About a 0.5 μm thick Mg-doped Al_(0.1)Ga_(0.9)N p-layer 61 was formed onthe emission layer 5 under conditions of lowering the temperature in thechamber to 1000° C., keeping the temperature constant and supplying N₂or H₂, NH₃. TMG, TMA, and CP₂Mg for 7 min. at a flow rate of 20liter/min., 10 liter/min., 1.12×10⁻⁴ mol/min., 0.47×10⁻⁴ mol/min., and2×10⁻⁷ mol/min., respectively. At this stage, the p-layer 61 remainedinsulative with a resistivity of 10⁸ Ω·cm or more. The impurityconcentration of the Mg-doped into the p-layer 61 was 1×10¹⁹/cm³.

Then, about a 0.5 μm thick Mg-doped GaN contact layer 62 was formed onthe p-layer 61 under conditions of lowering the temperature in thechamber to 1000° C., keeping the temperature constant and supplying N₂or H₂, NH₃, TMG, and CP₂Mg for 10 min. at a flow rate of 20 liter/min.,10 liter/min., 1.12×10⁻⁴ mol/min., and 2×10⁻⁴ mol/min., respectively. Atthis stage, the Mg-doped contact layer 62 remained insulative with aresistivity of 10⁸ Ω·cm or more. The impurity concentration of theMg-doped into the contact layer 62 was 1×10²⁰/cm³.

Then, the p-layer 61 and contact layer 62 were uniformly irradiated byan electron beam under the same conditions as described in Example 1.Consequently, the p-layer 61 and contact layer 62 are processed toexhibit p-type conduction with a 2×10¹⁷/cm³ hole concentration and 2Ω·cm or more resistivity. The subsequent process steps of forming theelectrodes is the same as that described in the previous example. As aresult, the LED 10 having a single hetero-junction structure is obtainedwhose emission layer is doped with Zn as an acceptor and Si as a donorimpurity. Alternatively, doping Mg and irradiating electrons into theemission layer 5 can be used to obtain an emission layer 5 with p-typeconduction.

Example 5

FIG. 11 shows a LED 10 embodied in this example. Three layers, a p-layer61, an emission layer 5, and an n⁺-layer 4, are unique to Example 5. Thep-layer 61 is formed of Mg-doped Al_(x1)Ga_(1-x1)N. The emission layer 5is Zn- and Si-doped Al_(x2)Ga_(1-x2)N. The n⁺-layer 4 of high carrierconcentration is Si-doped Al_(x3)Ga_(1-x3)N. Other layers and electrodesare formed the same as those described in Example 4. The compositionratio of x1, x2 and x3 in each layer is designed to make the band gap ofthe emission layer 5 smaller than those of the n⁺-layer 4 and p-layer 61forming a double hetero-junction structure or a single hetero-junctionstructure. Thanks to this structure, carriers are confined in theemission layer 5 contributing to higher luminous intensity. The emissionlayer 5 can exhibit any one of semi-insulative, p-type conductivity; orn-type conductivity.

Example 6

FIG. 12 shows a LED 10 embodied in this example. Three layers, a p-layer61, an emission layer 5, and an n⁺-layer 4, are unique to Example 6. Thep-layer 61 formed of Mg-doped Al_(x1)Ga_(1-x1)N. The emission layer 5 isformed of Zn- and Si-doped Ga_(y)In_(1-y)N. The n⁺-layer 4 of highcarrier concentration is formed of Si-doped Al_(x2)Ga_(1-x2)N. Otherlayers and electrodes are formed the same as those described in Example4. The composition ratio of x1, x2, and x3 in each layer is designed tomake the band gap of the emission layer 5 smaller than those of then⁺-layer 4 and p-layer 61 forming a double hetero-junction structure ora single hetero-junction structure. Thanks to this structure, carriersare confined in the emission layer 5 contributing to higher luminousintensity. The emission layer 5 can exhibit any one of semi-insulative,p-type conductivity, or n-type conductivity.

The LED 10 in this example has a sapphire substrate 1 which has thefollowing five layers are consecutively formed thereon: an AlN bufferlayer 2; a Si-doped Al_(x2)Ga_(1-x2)N n⁺-layer 4 of high carrier(n-type) concentration; a Zn- and Si-doped Ga_(0.94)In_(0.06)N emissionlayer 5, Mg-doped Al_(0.1)Ga_(0.9)N p-layer 61 of p-type, and anMg-doped GaN contact layer 62 of p-type. The AlN layer 2 has a 500 Åthickness. The Al_(x2)Ga_(1-x2)N n⁺-layer 4 has about a 4.0 μm thicknessand a 2×10¹⁸/cm³ electron concentration. The emission layer 5 has about0.5 μm thickness. The p-layer 61 has about a 0.5 μm thickness and a2×10¹⁷/cm³ hole concentration. The contact layer 62 has about a 0.5 μmthickness and a 2×10¹⁷/cm³ hole concentration. Nickel electrodes 7 and 8are formed to connect to the contact layer 62 and n⁺-layer 4 of highcarrier concentration, respectively. The two electrodes are electricallyinsulated by a groove 9.

A manufacturing process for the LED 10 of FIG. 12 is as follows. Thesapphire substrate 1 and the AlN buffer layer 2 were prepared by thesame process described in detail in Example 1. On the AlN buffer layer2, about a 4.0 μm thick Si-doped Al_(x2)Ga_(1-x2)N n⁻-layer 4 of highcarrier concentration with an electron concentration of 2×10¹⁸/cm³ wasformed under conditions of lowering the temperature in the chamber to1150° C., keeping it constant, and supplying N₂, NH₃, TMG, TMA, anddiluted silane to 0.86 ppm by H₂ for 60 min. at a flow rate of 20liter/min., 10 liter/min., 1.12×10⁻⁴ mol/min., 0.47×10⁻⁴ mol/min., and10×10⁻⁹ mol/min., respectively.

Following manufacturing process and composition ratio for the threelayers, the emission layer 5 as an active layer, the p-layer 61 as aclad layer, and the contact layer 62, show an example where the LED 10is designed to have 450 nm wavelength at peak in luminous spectrum andhave luminous centers of Zn and Si.

About a 0.5 μm thick Zn- and Si-doped Ga_(0.94)In_(0.06)N emission layer5 was formed on the n⁺-layer 4 under conditions of raising thetemperature in the chamber to 850° C., keeping it constant, andsupplying N₂ or H₂, NH₃, TMG, TMI, DMZ and, silane for 60 min. at a flowrate of 20 liter/min., 10 liter/min., 1.53×10⁻⁴ mol/min., 0.02×10⁻⁴mol/min., 2×10⁻⁷ mol/min., and 10×10⁻⁹ mol/min., respectively.

About a 0.5 μm thick Mg-doped Al_(0.1)Ga_(0.9)N p-layer 61 was formed onthe emission layer 5 under conditions of raising the temperature in thechamber to 1000° C., keeping the temperature constant and supplying N₂or H₂, NH₃, TMG, TMA, and CP₂Mg for 7 min. at a flow rate of 20liter/min., 10 liter/min., 1.12×10⁻⁴ mol/min., 0.47×10⁻⁴ mol/min., and2×10⁻⁷ mol/min., respectively. At this stage, the p-layer 61 remainedinsulative with a resistivity of 10⁸ Ω·cm or more. The impurityconcentration of the Mg doped into the p-layer 61 was 1×10¹⁹/cm³.

Then, about a 0.5 μm thick Mg-doped GaN contact layer 62 was formed onthe p-layer 61 under conditions of keeping the temperature in thechamber at 1000° C. and supplying N₂ or H₂, NH₃, TMG, and CP₂Mg for 10min. at a flow rate of 20 liter/min., 10 liter/min., 1.12×10⁻⁴ mol/min.,and 2×10⁻⁴ mol/min., respectively. At this stage, the Mg-doped contactlayer 62 remained insulative with a resistivity of 10⁸ Ω·cm or more. Theimpurity concentration of the Mg doped into the contact layer 62 was1×10²/cm³.

Then, the p-layer 61 and contact layer 62 were uniformly irradiated byan electron beam with the same conditions described in Example 1.Consequently, the p-layer 61 and contact layer 62 are processed toexhibit p-type conduction with a 2×10¹⁷/cm³ hole concentration and a 2Ω·cm resistivity. The subsequent process steps of forming the electrodesis the same as that described in the previous example.

In Examples 1 to 6, the emission layer 5 can exhibit any one ofsemi-insulation, p-type conductivity, or n-type conductivity. When theconcentration of the Zn-doped to the emission layer 5 is higher thanthat of the Si, the layer 5 exhibits semi-insulative characteristics.When the concentration of the Zn is smaller than that of the Si, theemission layer 5 exhibits n-type conduction.

In order to improve the luminous intensity, the impurity concentrationof Zn and Si doped to the emission layer 5 is preferably in the1×10¹⁷/cm³ to 1×10²⁰/cm³ range, respectively. The concentration is morepreferably in the 1×10¹⁸/cm³ to 1×10¹⁹/cm³ range. It is not preferablethat the impurity concentration be lower than 1×10¹⁸/cm³, because theluminous intensity of the LED decreases as a result. It is not desirablethat the impurity concentration is higher than 1×10¹⁹/cm³, because poorcrystallinity occurs. It is preferable that the concentration of Si isten to one-tenth as that of Zn. The most preferable concentration of Siis in the one to one-tenth range or closer to one-tenth to Zn.

In Examples 1 to 6, Cd, Zn, and Mg were employed as acceptor impuritiesand Si as a donor impurity. Alternatively, beryllium (Be) and mercury(Hg) can be used as an acceptor impurity. Alternatively, carbon (C),germanium (Ge), tin (Sn), lead (Pb), sulfur (S), selenium (Se), andtellurium (Te) can be used as a donor impurity.

Electron irradiation was used in Examples 1 to 6 in order to process anemission layer 5 to exhibit p-type conduction. Alternatively, annealing,heat processing in the atmosphere of N₂ plasma gas and laser irradiationcan be used.

Example 7

FIG. 14 shows a structural view of a LED 10 embodied in Example 7. TheLED 10 in this example was manufactured by additionally doping Mg to theemission layer 5 of the LED 10 in Example 1. Other layers and electrodeswere manufactured the same way as those described in Example 1.

CP₂Mg was fed at a flow rate of 2×10⁻⁷ mol/min. into a chamber inaddition to gasses employed in Example 1 in order to manufacture theemission layer 5 in Example 7. The emission layer 5 was about a 0.5 μmthick including Mg-, Cd-, and Si-doped(Al_(0.09)Ga_(0.91))_(0.99)In_(0.01)N remaining high insulative.Impurity concentration of the Mg. Cd and Si was 1×10²⁰/cm³, 5×10¹⁸/cm³,and 1×10¹⁸/cm³, respectively.

Then, electron beam was uniformly irradiated on both of the emissionlayer 5 and p-layer 6 with an electron diffraction device under the sameconditions as in Example 1. The emission layer 5 and p-layer 6 came toexhibit p-type conduction with a hole concentration of 2×10¹⁷/cm³ and aresistivity of 2 Ω·cm.

Example 8

FIGS. 15 and 16 show structural views of a LED 10 embodied in Example 8.The LED 10 in this example was manufactured by additionally doping Mgand irradiating electrons into the emission layer 5 of the LED 10 inExample 6. The emission layer 5 of Example 8 includes Mg-, Zn-, andSi-doped Ga_(y)In_(1-y)N exhibiting p-type conduction. Other layers andelectrodes were manufactured the same way as those described in Example1.

FIG. 16 shows an example where the LED 10 is designed to have a 450 nmwavelength at peak in the luminous intensity. The manufacturing processand composition equation of the three layers, the emission layer 5 as anactive layer, the p-layer 61 as a clad layer and the contact layer 62are described hereinafter.

The CP₂Mg was fed at a flow rate of 2×10⁻⁴ mol/min. into a chamber inaddition to gasses employed in Example 6 in order to manufacture theemission layer in Example 8. The emission layer 5 was about a 0.5 μmthick including Mg-, Zn-, and Si-doped Ga_(0.94)In_(0.06)N remaininghighly insulative.

Then, the emission layer 5, p-layer 61 and contact layer 61 wereuniformly irradiated by an electron diffraction device under the sameconditions as those described in Example 1. This irradiation changed theemission layer 5, p-layer 61, and contact layer 62 into layersexhibiting p-type conduction with a hole concentration of 2×10¹⁷/cm³ anda resistivity of 2 Ω·cm.

In Examples 7 and 8, the impurity concentration of Zn and Si doped intothe emission layer 5 are preferably in the 1×10¹⁷/cm³ to 1×20²⁰/cm³range, respectively. The concentration is more preferably in the1×10¹⁸/cm³ to 1×10¹⁹/cm³ range. It is not preferable that the impurityconcentration be lower than 1×10¹⁸/cm³, because luminous intensity ofthe LED decreases as a result. It is not desirable that the impurityconcentration be higher than 1×10¹⁹/cm³, because poor crystallinityoccurs. It is further preferable that the concentration of Si be ten toone-tenth as same as that of Zn. The most preferable concentration of Siis in the two to one-tenth range.

In Examples 7 and 8, Cd, Zn and Mg were employed as acceptor impuritiesand Si as a donor impurity. Alternatively, beryllium (Be) and mercury(Hg) can be used as an acceptor impurity. Alternatively, carbon (C),germanium (Ge), tin (Sn), lead (Pb), sulfur (S), selenium (Se) andtellurium (Te) can be used as a donor impurity.

Electron irradiation was used in Examples 7 and 8 in order to changelayers to have p-type conduction. Alternatively, annealing, heat processin the atmosphere of N₂ plasma gas, laser irradiation and anycombination thereof can be used.

While the invention has been described in connection with what arepresently considered to be the most practical and preferred embodiments,it is to be understood that the invention is not to be limited to thedisclosed embodiments, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

1. A method of producing a light-emitting semiconductor device of agroup III nitride compound, comprising: forming an N-layer of an N-typeconduction, said N-layer comprising gallium nitride; forming a highcarrier concentration N⁺-layer satisfying the formula(Al_(x3)Ga_(1-x3))_(y3)In_(1-y3)N, wherein 0≦x3≦1, 0≦y3≦1 and 0≦x3+y3≦1,on said N-layer; forming an emission layer of a group III nitridecompound semiconductor satisfying the formula,Al_(x1)Ga_(y1)In_(1-x1-y1)N, where 0≦x1≦1, 0≦y1≦1 and 0≦x1+y1≦1 on saidhigh carrier concentration layer N⁺-layer; doping Si and Zn into saidemission layer; forming a P-layer of a P-type conduction, on saidemission layer, said P-layer comprising aluminum gallium nitridesatisfying the formula Al_(x2)Ga_(1-x2)N, wherein 0≦x2≦1; and forming acontact layer of a P-type conduction, on said P-type layer, said contactlayer comprising gallium nitride.
 2. A semiconductor light emittingdevice comprising: an n-type clad layer consisting of a gallium nitridebase compound semiconductor; an active layer consisting of a galliumnitride based compound semiconductor, said active layer being made froma material having a band gap energy smaller than that of said n-typeclad layer; and a p-type clad layer consisting of a gallium nitridebased compound semiconductor, said p-type clad layer being made from amaterial having a band gap energy greater than that of said activelayer, and sandwiching said active layer accompanying with said n-typeclad layer, wherein said materials of said n-type clad layer and saidp-type clad layer are selected as to make a band gap energy of saidn-type clad layer smaller than the band gap energy of said p-type cladlayer.
 3. A semiconductor light emitting device comprising: a substrate;and GaN-type compound semiconductor layers stacked on the substrate, theGaN-type layers including: at least one active layer; at least onen-type layer; and at least one p-type layer, wherein a band gap energyof the one n-type layer is smaller than a band gap energy of the onep-type layer.